In 2013, U.S. District Judge G. Murray Snow found Arpaio’s office engaged in systemic racial profiling of Latinos in its anti-illegal-immigration efforts. Snow ordered the agency to stop detaining people solely because they were suspected of being undocumented.

Arpaio openly defied Judge Snow’s court order. As a result he was tried and convicted of criminal contempt of court. The Washington Post reported that Arpaio faced up to six months in prison and was scheduled for sentencing on October 5.

That changed last week. At a press conference, trying to justify the pardon, Trump said "He's (Arpaio) done a great job for the people of Arizona. He's very strong on borders, very strong on illegal immigration . . . I thought he was treated unbelievably unfairly."

Presidents have virtually unlimited power to grant clemency to individuals charged or convicted of a federal crime at any point in the legal process, even before they are charged with a crime. As Article II of the U.S. Constitution provides, the president can "grant Reprieves and Pardons for Offenses against the United States, except in Cases of Impeachment."

There’s no question that Trump had the legal standing to issue the pardon, but the circumstances of this — his first pardon — are strange to say the least.

Trump's pardon marks one of the earliest pardons in a president's term and one of the only pardons granted alone, according to a CNN analysis of Department of Justice data from the last 30 years.

A majority of presidential pardons have come in the last year of a president's term, they usually come in groups of a dozen or more and they set aside convictions averaging more than two decades old. Trump also ignored the process of having the Department of Justice make a recommendation on the pardon request.

Some people suggest that the pardon was meant to send a message. Maybe it was a sign to law enforcement "I got your back" or maybe it was a sign to his staff and advisors "I can protect you from Robert Mueller."

If the latter is true, Mueller just threw a wrench into that idea.

The presidential pardon only applies to federal crimes. Mueller is now coordinating with New York Attorney General Eric Schneiderman in the investigation of former Trump campaign manager Paul Manafort.

It is unclear whether Schneiderman is investigating any other New York-based Trump associates under scrutiny by the special counsel, such as Trump's son Donald Jr. or his son-in-law, Jared Kushner.

Mueller seems to be preparing for the "pardon" possibility by lining up "potential state prosecutions in states where these folks may have violated state law," Yale Law School dean Asha Rangappa told the Business Insider.

"There's a legal principle called 'dual sovereignty' [which] means that for purposes of criminal prosecution, the state and federal government are separate sovereigns [with] concurrent jurisdiction," Rangappa said. "[B]oth the federal government and a state can prosecute on the same set of facts if those facts would constitute a crime in their respective jurisdictions."

In July, the New York Times reported that President Trump asserted he had the "complete power to pardon" relatives, aides and possibly even himself in response to the Russia investigation. Trump can pardon anybody facing charges from Mueller, but not from Schneiderman. Mueller may be sending a message of his own to those close to Trump.

Trump’s "trump card" may have just disappeared. With the leverage of a pardon gone, those feeling the heat form Mueller and Schneiderman may be more willing to talk about Russia, the election and collusion.

— Matthew T. Mangino is of counsel with Luxenberg, Garbett, Kelly & George P.C. His book The Executioner’s Toll, 2010 was released by McFarland Publishing. You can reach him at www.mattmangino.com and follow him on Twitter @MatthewTMangino.